A user can perform activities including downloading and uploading data and/or carrying out a voice call. The activities, for example, can be done using a radio device, also known as a wireless device, which performs transactions via radio signals with a radio network. The format, timing, information-carrying ability and multi-user medium-sharing properties of the radio signals are the result of a particular radio access technology (RAT) employed by the wireless device and the radio network. A RAT can also be referred to as a radio interface. A problem arises when the user is away from home yet wishes to quickly establish a connection with a visited radio network so as to initiate a data transaction or receive a voice call. Use of a visited radio network is often referred to as roaming.
A given radio network is generally connected with other networks, such as the Internet. Data can be downloaded from, and uploaded, to sites or other parties via the Internet. The business entity that manages and/or provides the radio network can be referred to as a home wireless carrier with respect to the user and wireless device. Radio networks generally are characterized by a limited geographic footprint or coverage area. That is, when the user physically carries the wireless device away from the home radio network, the wireless device and the radio network are unable to successfully exchange information by radio with the home radio network. This may disappoint a user and lead to user dissatisfaction with their wireless device. The home wireless carrier can have business arrangements, known as roaming agreements, with other wireless carriers in other geographic regions. The roaming agreements allow the user to successfully communicate, via the radio network equipment of those other wireless carriers, by the user using their wireless device while away from their home radio network. Easy and affordable use of a wireless device to communicate while away from a home network will often result in user satisfaction.
In general, the wireless device may be referred to as a Mobile Subscriber (MS) or User Equipment (UE). The UE can include a Subscriber Identity Module (SIM), also known as a smart card, and/or the UE can include an electronic SIM (eSIM) and/or universal subscriber identity module (USIM). The application will refer to these generally with the term USIM. The USIM can be identified by an Integrated Circuit Card Identifier (ICCID). The USIM is within the control of the home wireless carrier, in the sense that only the home wireless carrier is in possession of the security secrets needed to gain access and read or write sensitive data from or to the USIM. The wireless phone number associated with a given USIM is also associated with an international mobile subscriber identity (IMSI). An embedded Universal Integrated Circuit Card (eUICC) in the UE can host the USIM.
Message flows that place data in a wireless device and/or in a network server need to be secure. Security has two main aspects: authentication and confidentiality. Authentication is the process of assuring the identity of the party that is asking to talk, the claimant. Confidentiality is maintained by not allowing unintended parties to read transmitted information. Authentication is often carried out using a challenge-response protocol. A challenger sends a challenge to the claimant. If the claimant is able to prove in its response possession of a particular secret, then the challenger is satisfied about the identity of the claimant. Confidentiality is maintained by encryption. A sending party encodes information with one or more keys, where those keys (or related keys) are known to the recipient. Keys may be frequently changed to limit loss of confidentiality due to a third party obtaining a particular key.
Travel of the user to a geographic region away from their home radio network is known as roaming. The home wireless carrier configures the wireless device to be able to find visited radio networks over which the wireless device can communicate when roaming by use of a roaming list. A roaming list is a list of geographic places and radio networks within those geographic places that have roaming agreements with the home wireless carrier. The roaming list can be stored in a USIM. In practice, the entries on the list include at least a place or geographic region identifier known as a mobile country code (MCC) and a wireless network identifier known as a mobile network code (MNC). The two identifiers taken together, MCC:MNC, are referred to as identifying a public land mobile network (PLMN). A given PLMN will often support more than one RAT. For example, a wireless carrier in Canada may support both GSM and Wi-Fi Calling.
A wireless device, on power-up, scans radio signals in search of the home radio network. A scan is a trial-and-error radio signal observation or measurement at various radio frequencies. If the measurement reveals the presence of significant radio energy, the wireless device attempts to decode information at the radio frequency and identify the source of the radio transmission. If the home radio network is not found, the wireless device performs scans at additional frequencies, based on the roaming list, in hopes of discovering some radio network. If some other radio network is found on a particular frequency, the wireless device obtains system information, and may continue to monitor the particular frequency and wait for the user to make a demand to communicate or receive data. System information generally includes network identification data. Such network monitoring while waiting for a user demand is referred to as camping. In some cases, the wireless device transmits the IMSI of the active USIM to the visited radio system in hopes of being accepted by the found radio system, i.e., registered with the found radio system, and progresses to communicating through the found radio system to other networks, such as the Internet. There is some uncertainty in the chances of success, in terms of acceptance, when transmitting to the visited radio system. For example, the IMSI may be rejected, or the found radio network may not allow roaming in some limited geographic area in which the wireless device happens to be. A benefit of registering is that incoming calls can be routed to the visited radio system and thence to the wireless device.
A wireless carrier may store, or provision, the roaming list in a USIM. A wireless carrier can update, or refresh, the roaming list using a procedure known as steering of roaming. The provisioning network entity may be a server and the USIM can be viewed as a client. Thus the SIM and the provisioning network entity may have a client-server relationship. The server can check the identity of a SIM using authentication techniques. The server can protect information, maintain confidentiality, sent to the SIM using encryption techniques.
More information on roaming can be found in, for example, “Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode,” 3GPP TS 23.122 version 13.4.0, March, 2016. More information on provisioning of eSIMs and USIMs can be found, for example, in “RSP Architecture,” Version 1.0, Dec. 23, 2015, GSM Association document SGP.21.